This application claims the priorities of German Application Nos. 197 20 857.6, filed May 17, 1997, 297 08 814.9, filed May 17, 1997, and 197 27 321.1, filed Jun. 27, 1997.
The present invention relates to a joint for torsion-proof connection of two shafts with one another such as the connection which is known, for example, from German Patent Document DE 43 04 274 C1.
When used in vehicles, joints of this type are severely stressed not only mechanically, by torque peaks and by overtensioning joint movements, but also thermally as a result of thermal conduction and heat radiation of very hot parts situated in the vicinity of the joints. In the case of plastic parts, the loadability of the materials used is reduced by the heating of the components so that the thermal stressing of the joints is also relevant to their mechanical loadability.
Many known joints, and particularly shafts of light-weight constructions, have respective flanges on the ends of the two shafts connected by the joint, which flanges have three driving pins axially projecting in the direction of the joint. In this case, six driving pins are arranged in a mutually staggered manner and are uniformly arranged on the circumference of a common graduated circle. The driving pins are connected with one another in a torsion-proof manner by a flexible hexagonal joint ring provided with sockets in its corner points. Between the sockets, the joint ring is itself axially elastically deformable so that the two flanges connected by the joint ring can carry out limited angular movements in any direction also during rotation. This angular movement axially undulates the joint ring so that within the scope of the elasticity, bending stresses occur corresponding to Hooke's law and are superimposed on the torque-caused operational stresses. As a result of this superimposition of stresses, the strength of the materials may be reached. Accordingly, because of the fatigue strength of the joints, only limited bending angles can be permitted.
Three driving pins per flange, resulting in a total of six driving pins in the joint, are not absolutely required. Using only two pins per flange, resulting in a total of four driving pins, is also conceivable. In this case, however, because of the distribution of the circumferential stress on the small number of driving pins, these driving pins are subjected to more stress than when a higher number of driving pins is used. The use of four or more pins per flange, resulting in a total of eight or more driving pins in the joint, is also conceivable. In this case, with the rising number of driving pins, the required joint diameter becomes larger and/or the tolerable bending angle becomes smaller. Therefore, three or six driving pins are frequently used as a compromise between stress on the components, on the one hand, and the joint size, on the other hand.
German Patent Document DE 41 40 311 A1 shows a hexagonal joint ring made of a fiber reinforced material in the form of a ring disk, in the case of which axial sockets are embedded in the reinforced corner areas. The linear areas between two adjacent corners are formed by a relatively thin web which extends in the plane of the ring disk and is made of several cohesive layers of hardened fiber reinforced material. This web is relatively wide in the radial direction. During bending of the joint, these webs are not only bent but also twisted. Although, in the case of relatively low bending stresses, the thin webs can be elastically bent, because the shape of the webs deviates considerably from rotational symmetry, during twisting of the webs, high tensions occur mainly at their interior and exterior edges.
The initially mentioned German Patent Document DE 43 04 274 C1 shows a hexagonal joint ring in which the sockets arranged in the corner areas are connected, in pairs, to one another by oval driving loops which themselves are closed and are wound on the outside around two adjacent sockets. Specifically, wide centrally located driving loops and a pair of driving loops situated on an edge side are alternately arranged in the joint ring. The wide driving loop is approximately three times as wide as its radial wall thickness; the two narrow driving loops together are approximately as wide as the driving loop situated in the center. The driving loops are radially swivellable on the sockets so that, as an individual component, the shape of the joint ring can be flexibly changed. For holding all parts of the joint ring together and for preventing the entry of dirt, the parts of the joint ring are embedded in a rubber-elastic mass of low hardness and are completely enclosed. Because the radial wall thickness is relatively narrow in relation to the axially measured width of the driving loops, they offer good prerequisites for absorbing circumferential tension when low excess tensions in the curvatures of the driving loops are present. However, during bending of this joint, the driving loops are tilted and also twisted, in which case high excess tensions occur at different points of the driving loops. During tilting, there is a one-sided edge support of the loop curvature on the socket which results in a concentration of tension at this location. During twisting of the relatively wide driving loops, in a manner similar to that of the webs of the joint disk according to German Patent Document DE 41 40 311 A1, excessive tensions occur at the edges although at a lower level than in the disk according to this document. Therefore, even under a moderate torque load, in operation, locally high tensions occur in the driving loops at least when noticeable bends of the joint reduce the nominal loading of the joint which can be tolerated over time.
It is an object of the invention to improve the joint of the above-mentioned type such that higher, durably reliable torque loads and/or bending angles can be permitted.
This object is achieved in joints according to the invention by a joint for torsion-proof connection of two shafts with one another which is axially and/or angularly movable within certain limits. The joint includes flanges which are, in each case, arranged at ends of the two shafts connected by the joint. Three driving pins axially project in the direction of the joint on each of the flanges to provide six mutually staggered driving pins uniformly arranged on a circumference of a common graduated circle. A flexible, regularly polygon-type, preferably hexagonal joint ring connects the driving pins with one another in a torsion-proof manner and is provided with sockets at corner points. The joint ring is axially elastically deformable between the sockets and is formed in several parts by a collar of several closed oval driving loops. Each of the loops winds around two adjacent sockets and can be radially swivelled on the sockets so that a shape of the joint ring can be changed in a flexible manner.
One linear compression bar is respectively mounted in an interior of each of the oval driving loops. The compression bar is provided on its two front ends at least indirectly with a supporting surface adapted to the sockets. Because of the compression bars in the interior of the receiving loops, a total of twice as many force transmission elements provide support in each loading direction as driving loops are provided for one rotating direction, respectively. In other words, as many force transmission elements are supportive as driving pins are contained in the joint. Specifically, each second driving loop in each loading direction is still supportive, but, in addition, the compression bars which are situated in-between and are arranged in the unloaded driving loops are also supportive. Because the force transmission elements are doubled, in comparison to the state of the art, a clearly higher nominal load of the joint can be durably permitted.
Further features and advantages of the invention will become clear. In addition, the invention will be described in connection with certain embodiments which are illustrated in the drawings.